The trigeminovascular system and migraine: studies characterizing cerebrovascular and neuropeptide changes seen in humans and cats

Messenger molecules and receptor mRNA in the human trigeminal ganglion

The presence and distribution of neuromessenger molecules and receptor mRNA in human trigeminal ganglion was studied with immunocytochemical, in situ hybridisation and RT-PCR techniques. Immunofluorescence staining revealed that calcitonin gene-related peptide (CGRP) immunoreactive (-ir) neurons occurred in high numbers, constituting 36-40% of all nerve cell bodies in the ganglion. Accordingly, in situ hybridisation demonstrated CGRP mRNA in a large portion of the trigeminal neurons. A small number of the nerve cell bodies showed substance P (SP)-ir, (18%), nitric oxide synthase (NOS)-ir (15%), and pituitary adenylate cyclase activating peptide (PACAP)-ir (20%). Double immunostaining revealed that only few CGRP-ir neurons also were NOS-ir (less than 5%). The C-terminal flanking peptide of neuropeptide Y, C-PON, was not visible in any of the nerve cell bodies studied. Agarose gel electrophoresis of the RT-PCR products from the ganglia demonstrated the presence of mRNA corresponding to CGRP1, NPY Y1 and Y2, and VIP1 receptors. These results suggest both sympathetic and parasympathetic influence on the activity in the trigeminal ganglion.

Regulation of calcitonin gene-related peptide secretion by a serotonergic antimigraine drug

We have investigated the regulation of calcitonin gene-related peptide (CGRP) release from trigeminal neurons by the serotonergic antimigraine drug sumatriptan. Serum levels of the neuropeptide CGRP are elevated during migraine. Treatment with the drug sumatriptan returns CGRP levels to normal coincident with the alleviation of headache. However, despite this clinical efficacy, the cellular target and mechanism of sumatriptan action are not well understood beyond the pharmacology of its recognition of the 5-HT1 class of serotonin receptors. We have used cultured trigeminal neurons to demonstrate that sumatriptan can directly repress CGRP secretion from sensory neurons. The stimulated secretion in response to depolarization or inflammatory agents was inhibited, but not the basal secretion rate. Unexpectedly, sumatriptan did not lower cAMP levels, in contrast to the classical role ascribed to the 5-HT1 receptors. Instead, activation of 5-HT1 receptors caused a slow and remarkably prolonged increase in intracellular calcium. The inhibition of CGRP secretion is attenuated by the phosphatase inhibitor okadaic acid, suggesting that sumatriptan action is mediated by calcium-recruited phosphatases. These results suggest that 5-HT1 agonists may block a deleterious feedback loop in migraine at the trigeminal neurons and provide a general mechanism by which this class of drugs can attenuate stimulated neuropeptide release.

Stimulation of the middle meningeal artery leads to Fos expression in the trigeminocervical nucleus: a comparative study of monkey and cat

The pain of a migraine attack is often described as unilateral, with a throbbing or pulsating quality. The middle meningeal artery (MMA) is the largest artery supplying the dura mater, is paired, and pain-producing in humans. This artery, or its branches, and other large intracranial extracerebral vessels have been implicated in the pathophysiology of migraine by theories suggesting neurogenic inflammation or cranial vasodilatation, or both, as explanations for the pain of migraine. Having previously studied in detail the distribution of the second order neurons that are involved in the transmission of nociceptive signals from intracranial venous sinuses, we sought to compare the distribution of second order neurons from a pain-producing intracranial artery in both monkey and cat. By electrically stimulating the middle meningeal artery in these species and using immunohistochemical detection of the proto-oncogene Fos as a marker of neuronal activation, we have mapped the sites of the central trigeminal neurons which may be involved in transmission of nociception from intracranial extracerebral arteries. Ten cats and 3 monkeys were anaesthetised with alpha-chloralose and the middle meningeal artery was isolated following a temporal craniotomy. The animals were maintained under stable anaesthesia for 24 h to allow Fos expression due to the initial surgery to dissipate. Following the rest period, the vessel was carefully lifted onto hook electrodes, and then left alone in control animals (cat n = 3), or stimulated (cat n = 6, monkey n = 3). Stimulation of the left middle meningeal artery evoked Fos expression in the trigeminocervical nucleus, consisting of the dorsal horn of the caudal medulla and upper 2 divisions of the cervical spinal cord, on both the ipsilateral and contralateral sides. Cats had larger amounts of Fos expressed on the ipsilateral than on the contralateral side. Fos expression in the caudal nucleus tractus solitarius and its caudal extension in lamina X of the spinal cord was seen bilaterally in response to middle meningeal artery stimulation. This study demonstrates a comparable anatomical distribution of Fos activation between cat and monkey and, when compared with previous studies, between this arterial structure and the superior sagittal sinus. These data add to the overall picture of the trigeminovascular innervation of the intracranial pain-producing vessels showing marked anatomical overlap which is consistent with the often poorly localised pain of migraine.

Capsaicin-insensitive sensory-efferent meningeal vasodilatation evoked by electrical stimulation of trigeminal nerve fibres in the rat

1. Antidromic vasodilatation and plasma extravasation to stimulation of the trigeminal ganglion or its perivascular meningeal fibres was investigated by laser-Doppler flowmetry and 125I-labelled bovin serum albumin in the dura mater and in exteroceptive areas (nasal mucosa, upper eyelid) of anaesthetized rats pretreated with guanethidine and pipecuronium. 2 Trigeminal stimulation at 5 Hz for 20 s elicited unilateral phasic vasodilatation in the dura and lasting response in the nasal mucosa. Resiniferatoxin (1-3 microg kg(-1) i.v.), topical (1%) or systemic capsaicin pretreatment (300 mg kg(-1) s.c. plus 1 mg kg(-1) i.v.) did not inhibit the meningeal responses but abolished or strongly inhibited the nasal responses. Administration of vinpocetine (3 mg kg(-1) i.v.) increased both basal blood flow and the dural vasodilatation to perivascular nerve stimulation. 3. Dural vasodilatation to trigeminal stimulation was not inhibited by the calcitonin gene-related peptide-1 receptor (CGRP-1) antagonist hCGRP8-37 (15 or 50 microg kg(-1) i.v), or the neurokinin-1 receptor antagonist RP 67580 (0.1 mg kg(-1) i.v.) although both antagonists inhibited the nasal response. Neither mucosal nor meningeal responses were inhibited by atropine (5 mg kg(-1) i.v.), hexamethonium (10 mg kg(-1) i.v.) or the vasoactive intestinal polypeptide (VIP) antagonist (p-chloro-D-Phe6-Leul7)VIP (20 microg kg(-1) i.v.). 4. Plasma extravasation in the dura and upper eyelid elicited by electrical stimulation of the trigeminal ganglion was almost completely abolished in rats pretreated with resiniferatoxin (3 microg kg(-1) i.v.). 5. It is concluded that in the rat meningeal vasodilatation evoked by stimulation of trigeminal fibres is mediated by capsaicin-insensitive primary afferents, while plasma extravasation in the dura and upper eyelid and the vasodilatation in the nasal mucosa are mediated by capsaicin-sensitive trigeminal fibres.

Release of substance P, calcitonin gene-related peptide and prostaglandin E2 from rat dura mater encephali following electrical and chemical stimulation in vitro

Neurogenic inflammation of the dura, expressed in plasma extravasation and vasodilatation, putatively contributes to different types of headache. A novel in vitro preparation of the fluid-filled skull cavities was developed to measure mediator release from dura mater encephali upon antidromic electrical stimulation of the trigeminal ganglion and after application of a mixture of inflammatory mediators (serotonin, histamine and bradykinin, 10(-5) M each, pH 6.1) to the arachnoid side of rat dura. The release of calcitonin gene-related peptide, substance P and prostaglandin E2 from dura mater was measured in 5-min samples of superfusates using enzyme immunoassays. Orthodromic chemical and antidromic electrical stimulation of dural afferents caused significant release of calcitonin gene-related peptide (2.8- and 4.5-fold of baseline). The neuropeptide was found to be increased during the 5-min stimulation period and returned to baseline (20.9 +/- 12 pg/ml) in the sampling period after stimulation. In contrast, release of substance P remained at baseline levels (19.3 +/- 11 pg/ml) throughout the experiment. Prostaglandin E2 release was elevated during chemical and significantly also after antidromic electrical stimulation (6- and 4.2-fold of baseline, which was 305 +/- 250 pg/ml). Prostaglandin E2 release outlasted the stimulation period for at least another 5 min. The data support the hypothesis of neurogenic inflammation being involved in headaches and provide new evidence for prostaglandin E2 possibly facilitating meningeal nociceptor excitation and, hence, pain.

Serotonin in migraine: theories, animal models and emerging therapies

A role for serotonin in migraine has been supported by changes in circulating levels of serotonin and its metabolites during the phases of a migraine attack, along with the ability of serotonin-releasing agents to induce migraine-like symptoms. The development of serotonin receptor agonists with efficacy in the clinic for the alleviation of migraine pain further implicates serotonin as a key molecule in migraine. Several theories regarding the etiology of migraine have been proposed. The vasodilatory theory of migraine suggested that extracranial arterial dilation during an attack was related to migraine pain; a theory supported when vasoconstrictors such as sumatriptan alleviated migraine pain. The neurological theory of migraine proposed that migraine resulted from abnormal firing in brain neurons. Cortical spreading depression, one facet of the neurological theory, could explain the prodrome of migraine. The neurogenic dural inflammation theory of migraine supposed that the dural membrane surrounding the brain became inflamed and hypersensitive due to release of neuropeptides from primary sensory nerve terminals. Substance P, calcitonin gene related peptide and nitric oxide are all though to play a role in the dural inflammatory cascade. Animal models of migraine have been utilized to study the physiology of migraine and develop new pharmaceutical therapies. One model measures the shunting of blood to arteriovenous anastomoses based on a proposal that migraine primarily involves cranial arteriovenous vasodilation. Another model utilizes electrical stimulation of the trigeminal ganglion to induce neurogenic dural inflammation quantified by the resulting extravasation of proteins. Pharmacological agents such as meta-chlorophenylpiperazine (mCPP) and nitroglycerin have also been used to induce dural extravasation in animals. Both compounds also induce migraine attacks in individuals with a history of migraine. In addition, Fos, a protein produced by activation of the c-fos gene, has been measured as an index of migraine-like pain transmission to the CNS following chemical or electrical stimulation of the trigeminal nerve. A role for serotonin in migraine is further supported by the efficacy of serotonin receptor ligands. Sumatriptan is an agonist at 5-HT1D and 5-HT1B receptor subtypes, and effective in treating migraine pain and associated symptoms. Recently, selective 5-HT1F agonists have been proposed for the treatment of migraine, without the side effects associated with the present 5-HT1D and 5-HT1B receptor agonists. A role for 5-HT2B receptors has also been suggested the initiation of migraine, supporting use of selective 5-HT2B receptor antagonists in migraine. Thus, agents that modulate 5-HT1B, 5-HT1D, 5-HT1F and 5-HT2B receptors either have or may have clinical utility in the therapy of migraine headache.

The trigeminovascular system in humans: pathophysiologic implications for primary headache syndromes of the neural influences on the cerebral circulation

Primary headache syndromes, such as cluster headache and migraine, are widely described as vascular headaches, although considerable clinical evidence suggests that both are primarily driven from the brain. The shared anatomical and physiologic substrate for both of these clinical problems is the neural innervation of the cranial circulation. Functional imaging with positron emission tomography has shed light on the genesis of both syndromes, documenting activation in the midbrain and pons in migraine and in the hypothalamic gray in cluster headache. These areas are involved in the pain process in a permissive or triggering manner rather than as a response to first-division nociceptive pain impulses. In a positron emission tomography study in cluster headache, however, activation in the region of the major basal arteries was observed. This is likely to result from vasodilation of these vessels during the acute pain attack as opposed to the rest state in cluster headache, and represents the first convincing activation of neural vasodilator mechanisms in humans. The observation of vasodilation was also made in an experimental trigeminal pain study, which concluded that the observed dilation of these vessels in trigeminal pain is not inherent to a specific headache syndrome, but rather is a feature of the trigeminal neural innervation of the cranial circulation. Clinical and animal data suggest that the observed vasodilation is, in part, an effect of a trigeminoparasympathetic reflex. The data presented here review these developments in the physiology of the trigeminovascular system, which demand renewed consideration of the neural influences at work in many primary headaches and, thus, further consideration of the physiology of the neural innervation of the cranial circulation. We take the view that the known physiologic and pathophysiologic mechanisms of the systems involved dictate that these disorders should be collectively regarded as neurovascular headaches to emphasize the interaction between nerves and vessels, which is the underlying characteristic of these syndromes. Moreover, the syndromes can be understood only by a detailed study of the cerebrovascular physiologic mechanisms that underpin their expression.

Cardiovascular and neuronal responses to head stimulation reflect central sensitization and cutaneous allodynia in a rat model of migraine

Reduction of the threshold of cardiovascular and neuronal responses to facial and intracranial stimulation reflects central sensitization and cutaneous allodynia in a rat model of migraine. Current theories propose that migraine pain is caused by chemical activation of meningeal perivascular fibers. We previously found that chemical irritation of the dura causes trigeminovascular fibers innervating the dura and central trigeminal neurons receiving convergent input from the dura and skin to respond to low-intensity mechanical and thermal stimuli that previously induced minimal or no responses. One conclusion of these studies was that when low- and high-intensity stimuli induce responses of similar magnitude in nociceptive neurons, low-intensity stimuli must be as painful as the high-intensity stimuli. The present study investigates in anesthetized rats the significance of the changes in the responses of central trigeminal neurons (i.e., in nucleus caudalis) by correlating them with the occurrence and type of the simultaneously recorded cardiovascular responses. Before chemical stimulation of the dura, simultaneous increases in neuronal firing rates and blood pressure were induced by dural indentation with forces >/= 2.35 g and by noxious cutaneous stimuli such as pinching the skin and warming > 46 degrees C. After chemical stimulation, similar neuronal responses and blood pressure increases were evoked by much smaller forces for dural indentation and by innocuous cutaneous stimuli such as brushing the skin and warming it to >/= 43 degrees C. The onsets of neuronal responses preceded the onsets of depressor responses by 1.7 s and pressor responses by 4.0 s. The duration of neuronal responses was 15 s, whereas the duration of depressor responses was shorter (5.8 s) and pressor responses longer (22.7 s) than the neuronal responses. We conclude that the facilitated cardiovascular and central trigeminal neuronal responses to innocuous stimulation of the skin indicate that when dural stimulation induces central sensitization, innocuous stimuli are as nociceptive as noxious stimuli had been before dural stimulation and that a similar process might occur during the development of cutaneous allodynia during migraine.

Effect of a nitric oxide donor on nitroxergic nerve fibers in the rat dura mater

Nitroglycerine, given subcutaneously to rats (10 mg/kg body weight) induces increased beading of nitric oxide synthase immunoreactive (NOS-IR) nerve fibers in the supratentorial cerebral dura mater, and an apparent increase in the number of NOS-IR nerve fibers in the dural areas supplied by the anterior and middle meningeal arteries, and the sinus sagittalis superior. Structural alterations of nitroxergic axons innervating blood vessels of the dura mater support the idea that nitric oxide is involved in the induction of headache also by a primary peripheral action, a well-known side effect of coronary dilator agents.

Trigeminal nerve ganglion stimulation-induced neurovascular reflexes in the anaesthetized cat: role of endothelin(B) receptors in carotid vasodilatation

1. The effects of intravenous administration of endothelin (ET) receptor antagonists SB-209670 (0.001-10.0 mg kg(-1)), SB-217242, SB-234551 (0.01-10.0 mg kg(-1)) and BQ-788 (0.001-1.0 mg kg(-1)) were investigated on trigeminal nerve ganglion stimulation-induced neurovascular reflexes in the carotid vasculature of the anaesthetized cat. Comparisons were made with sumatriptan (0.003-3.0 mg kg(-1)) and alpha-CGRP8-37 (0.001-0.1 mg kg(-1)). 2. Trigeminal nerve ganglion stimulation produced frequency related increases in carotid blood flow, reductions in carotid vascular resistance and non-frequency related increases in blood pressure. Guanethidine (3 mg kg(-1), i.v.) blocked trigeminal nerve ganglion-induced increases in blood pressure but had no effect on changes in carotid flow or resistance. Maximal reductions in carotid vascular resistance was observed at 10 Hz, and this frequency was selected to investigate the effects of drugs on trigeminal nerve ganglion stimulation-induced responses in guanethidine treated cats. 3. Saline, alpha-CGRP8-37 SB-209670 and BQ-788 had little or no effect on resting haemodynamic parameters. SB-217242 (10 mg kg(-1), n=3) produced a 56% reduction in arterial blood pressure whereas SB-233451 (10 mg kg(-1), n=3) produced a 30% reduction in carotid vascular resistance. Sumatriptan produced dose-related reductions in resting carotid flow and increases (max. 104% at 0.3 mg kg(-1), n = 5) in vascular resistance. 4. SB-209670 (n=6-7), SB-217242 (n=3) and BQ-788 (n=3) produced inhibition of trigeminal nerve ganglion stimulation-induced reductions in carotid vascular resistance. Saline, SB-234551, alpha-CGRP8-37 and sumatriptan had no effect. 5. These data demonstrate ET(B) receptor blockade attenuates the vasodilator effects of trigeminal nerve ganglion stimulation in the carotid vascular bed of guanethidine pretreated anaesthetized cats.

A sensitive sandwich enzyme immunoassay for calcitonin gene-related peptide (CGRP): characterization and application

Thirty mouse monoclonal antibodies (mAbs) directed against rat calcitonin gene-related peptide-alpha (CGRP-alpha) have been obtained. These mAbs are classified in 2 groups, one recognizing the peptide N-terminus and the other binding the C-terminus. A two-site immunometric assay was developed using mAb CGRP-83 as capture antibody, whereas mAb CGRP-72 acts as tracer, covalently labeled with enzyme acetylcholinesterase. This assay appeared sensitive (limit of detection: 2 pg/ml) and precise, allowing quantitative measurement of all human and murine CGRP isoforms. The assay was used to determine specific concentrations of CGRP in different rat, mice and guinea pig samples. The validity of the test was demonstrated by HPLC fractionation experiments.

Release of immunoreactive substance P in the brain stem upon stimulation of the cranial dura mater with low pH - inhibition by the serotonin (5-HT1) receptor agonist CP 93,129

1. The therapeutical benefit of serotonin (5-HT1) receptor agonists in the treatment of migraine headache has been attributed to their inhibitory effect on the release of pro-inflammatory neuropeptides from trigeminal afferents within the cranial meninges. The effect of 5-HT1 receptor agonists on the release of neuropeptides from central afferent terminals has not been examined so far. In the present study in the rat we therefore measured the effect of the 5-HT1B receptor agonist CP 93,129 on the stimulation-evoked release of immunoreactive substance P (ir-SP) in the spinal trigeminal nucleus. 2. To measure release of ir-SP, microprobes coated with antibody to substance P were inserted into the medulla oblongata at the level of the obex. The ipsilateral parietal dura mater encephali was exposed and stimulated with acid phosphate buffered Tyrode solution (pH 5.8). This chemical stimulus increased the release of ir-SP in the medullary dorsal horn. 3. Systemic (i.v.) administration of CP 93,129 (460 nmol kg(-1)) prior to stimulation suppressed the stimulation-evoked increase of release of ir-SP. Local administration of CP 93,129 (10 microM) to the dorsal surface of the medulla had no significant inhibitory effect on the release. 4. It is concluded that systemically applied 5-HT1 receptor agonists reduce the stimulation-evoked release of substance P from the central endings of meningeal afferents in the spinal trigeminal nucleus (medullary dorsal horn). This inhibitory effect may contribute to the antinociceptive effect of 5-HT1 receptor agonists in migraine.

Cranial vascular effects of zolmitriptan, a centrally active 5-HT1B/1D receptor partial agonist for the acute treatment of migraine

The anti-migraine drug zolmitriptan is a novel 5-HT1B/1D receptor partial agonist which, unlike sumatriptan, has been shown to cross the intact blood-brain barrier. In this study we examined whether or not the ability to access the cerebro-vascular intima affects the way in which a centrally-active 5-HT1B/1D receptor agonist influences cranial haemodynamics. The effects of zolmitriptan on carotid arterial blood flow distribution were studied in anaesthetised cats using radiolabelled microspheres. Zolmitriptan (10-1000 microg kg(-1) i.v.) selectively reduced arteriovenous-anastomotic (AVA) conductance producing a maximum decrease of 92.5+/-2.3%. The drug also produced a modest reduction in extra-cerebral conductance (23.9+/-6.5% maximum reduction at 30 microg kg(-1), i.v.), but was without effect on cerebral conductance. Using laser doppler flowmetry in anaesthetised cats, zolmitriptan (1-30 microg kg(-1), i.v.) produced dose-dependent decreases in ear microvascular conductance (15+/-5 to 60+/-6%) which mirrored decreases in carotid arterial conductance (12+/-11 to 61+/-5%). By contrast, zolmitriptan at doses up to 1000 microg kg(-1) was without effect on cerebral microvascular conductance. Although zolmitriptan crosses the blood-brain barrier and can therefore access the cerebro-vascular intima, this study suggests that this property does not adversely affect cerebrovascular function.

A practical guide to the management and prevention of migraine

Migraine is a paroxysmal disorder with attacks of headache, nausea, vomiting, photo- and phonophobia and malaise. Mild migraine attacks are treated with antiemetics followed by analgesics such as aspirin (acetylsalicylic acid), paracetamol (acetaminophen) or nonsteroidal anti-inflammatory drugs (NSAIDs). Moderate to severe attacks are treated by antiemetics combined with ergotamine or dihydroergotamine. Sumatriptan, a specific serotonin 5-HT1B/D receptor agonist, is used if attacks do not respond to ergotamine or if intolerable adverse effects occur. The new migraine drugs zolmitriptan, naratriptan, rizatriptan and eletriptan differ in their pharmacological profile from sumatriptan, but this translates into only minor differences in efficacy, headache recurrence and adverse effects. Migraine prophylaxis should be implemented when more than 3 attacks occur per month, if attacks do not respond to acute treatment or if the adverse effects of acute treatment are severe. Substances with proven efficacy include the beta-blockers metoprolol and propranolol and the calcium antagonist flunarizine. Drugs less effective or those with unpleasant adverse effects are the serotonin receptor antagonists (pizotifen, methysergide and lisuride), dihydroergotamine, cyclandelate, NSAIDs, valproic acid (sodium valproate) and amitriptyline. The efficacy of aspirin or magnesium is still under evaluation.

Endothelin in migraine patients

Endothelins (ETs) are the most potent vasoconstrictors known, and may be the mediators of the vasoconstrictive phase in migraine attacks. We studied 31 previously selected migraine patients with (9) and without (22) aura ictally and interictally to determine their plasma ET-1 values. The mean interictal and ictal values were 5.3 pg/ml (SD 1.8) and 6.4 pg/ml (SD 3.9), respectively. The ictal values were markedly elevated at the beginning of the migraine attack (<2 h) and declined to interictal or even lower level later (4 to 6 h) in the course of an attack. The local vasoconstriction at the beginning of a migraine attack might be ET-mediated secondarily to serotonin activation.

Serotonin inhibits trigeminal nucleus activity evoked by craniovascular stimulation through a 5HT1B/1D receptor: a central action in migraine?

The development of serotonin (5HT1B/1D) agonists as treatments for the acute attack of migraine has resulted in considerable interest in their mechanism of action and, to some extent, renewed interest in the role of serotonin (5-hydroxytryptamine; 5HT) in the disorder. The initial synthesis of this class of compounds was predicated on the clinical observation that intravenous 5HT terminated acute attacks of migraine. In this study the superior sagittal sinus was isolated in the alpha-chloralose (60 mg/kg i.p. and 20 mg/kg i.v. injection supplementary 2 hourly) anesthetized cat. The sinus was stimulated electrically (120V, 250 microsec duration, 0.3 Hz), and neurons of the trigeminocervical complex in the dorsal C2 spinal cord were monitored using electrophysiological methods. After baseline recordings in each animal, 5HT (15 microg/kg/min) was infused for 5 minutes in the presence of either vehicle (group A) or the 5HT1B/1D antagonist GR127935 (100 microg/kg i.v. injection; group B). The baseline probability of cell firing after sagittal sinus stimulation was 0.61 +/- 0.1 at a latency to the fastest peak of 11.1 +/- 0.4 msec. In group A, 5HT infusion alone had a small effect of increasing mean blood pressure (12 +/- 3 mm Hg), which in itself did not alter cell firing. In group A, 5HT alone had an inhibitory effect on evoked trigeminal activity, which developed 15 to 20 minutes after commencement of the infusion. The inhibition of cell firing lasted for 20 minutes, after which the activity returned to baseline. In group B, the combination of 5HT and GR127935 had no effect on trigeminal cell firing, although the small hypertensive effect was still present. These data indicate that 5HT inhibits evoked trigeminal nucleus firing via the 5HT1B/1D receptor at which GR127935 is an antagonist. It is likely that some part of the effect of 5HT in migraine relates to inhibition of trigeminal nucleus activity, just as it is likely that some part of the effect of the triptans is also mediated at this central site and may be complementary to their nonneuronal actions. Moreover, the data highlight the case for describing this class of headache as neurovascular headaches rather than vascular headaches, to recognize the implicit contribution of the trigeminovascular system to their pathophysiology.

Perivascular nerves contribute to cortical spreading depression-associated hyperemia in rats

We investigated the contribution of perivascular nerves and neurotransmitters to cortical spreading depression (CSD)-associated hyperperfusion in the rat. Chronic transection of the nasociliary nerve (NCN, 2 wk before) decreased ipsilateral CSD-associated hyperperfusion by 23 +/- 13% (mean +/- SD; n = 5, P < 0.05), whereas acute transection of the NCN or sham surgery had no effect (n = 8). When the NCN and parasympathetic nerve fibers (PSN) were both chronically transected, CSD hyperperfusion was attenuated by 55 +/- 19% (n = 5, P < 0.05). Cerebrovascular reactivity to hypercapnia was not significantly affected. Brain topical superfusion of the muscarinic receptor antagonist atropine (10(-4) M) caused a reduction of CSD hyperperfusion by 41 +/- 13% (n = 5, P < 0.05). The competitive blockade of calcitonin gene-related peptide (CGRP) receptors by CGRP-(8-37) (5 x 10(-7) M) afforded a decrease by 49 +/- 19% (n = 5, P < 0.05), without affecting CO2 reactivity (n = 4). The combined application of both CGRP-(8-37) and atropine further attenuated CSD hyperperfusion (by 69 +/- 17%, n = 5, P < 0.05). After chronic NCN and PSN transection brain topical superfusion of CGRP-(8-37) (5 x 10(-7) M) reduced CSD hyperperfusion slightly by 9.5 +/- 5% (n = 3). Atropine (10(-4) M) afforded a decrease by 17 +/- 6% (n = 3). These reductions were not statistically significant. We conclude that CSD-associated hyperperfusion is mediated in part by a depolarization of trigeminal sensory and parasympathetic nerve fibers, resulting in a release of vasoactive trigeminal and parasympathetic neurotransmitters.

A fluorescence-based method for assessing dural protein extravasation induced by trigeminal ganglion stimulation

Neurogenic dural inflammation has been proposed as a source of pain during migraine. Unilateral electrical stimulation of the trigeminal ganglion causes the ipsilateral release of inflammatory neuropeptides and subsequent dural plasma protein extravasation, a component of neurogenic inflammation. We measured the amount of protein leaking into the dural tissue of guinea pigs following trigeminal ganglion stimulation by exploiting the complexation reaction of endogenous proteins with the fluorescent dye Evans Blue, instead of utilizing exogenous radiolabeled albumin as commonly done in the literature. The amount of Evans Blue trapped in dural tissue following electrical stimulation of the trigeminal ganglion was measured using a fluorescence microscope equipped with a spectrophotometer. This method utilized multiple measurements on each dura sample which resulted in very precise values using a small number of animals per point (n = 3). Sumatriptan and CP-122,288 were found to dose-dependently prevent neurogenic dural extravasation. The potencies of CP-122,288 and sumatriptan were found to be similar to those reported in the literature when similar experimental protocols were used.

Calcitonin gene-related peptide and nitric oxide in the trigeminal ganglion: cerebral vasodilatation from trigeminal nerve stimulation involves mainly calcitonin gene-related peptide

Nitric oxide (NO) is a novel neurotransmitter candidate to which a large number of physiological roles has been ascribed. In the present study, immunocytochemistry was used to demonstrate NO synthase (NOS) and to investigate possible co-localization with other neurotransmitters. In the trigeminal ganglion of the cat, a moderate number of NOS immunoreactive nerve cell bodies was seen, of which the major part also expressed calcitonin gene-related peptide (CGRP). The nerve cell bodies expressing NOS in the trigeminal ganglion were predominantly of small to medium size; while numerous cell bodies of varying size contained CGRP. With in situ hybridization using oligonucleotide probes, CGRP mRNA was demonstrated in almost all trigeminal neurons of the cat. Stimulation of the nasociliary nerve resulted in a frequency-dependent increase in ipsilateral local cortical blood flow by 30 +/- 6%. Administration of the NOS inhibitor NG-nitro-L-arginine-methylester (L-NAME) did not significantly alter this response when applied intravenously or on the cortical surface. Local cortical administration of the CGRP blocker h-CGRP (8-37) did not alter the cerebral vasodilator response to hypercapnia or resting flow. However, the nasociliary nerve response was reduced by 50% after h-CGRP (8-37), with a general shift to the right of the frequency-response curve. These data suggest that although NOS is seen in several trigeminal ganglion cells and coexists with CGRP in a subpopulation of the sensory neurons, its role in trigeminally mediated vasodilatation was not significant.

Site-directed mutagenesis of the human 5-HT1B receptor

Site-directed mutagenesis was used to investigate the molecular interactions involved in ligand binding to the human 5-HT1B receptor. Six mutants were constructed at four positions and expressed in Chinese hamster ovary cells. Substitution of the amino acid F185 in transmembrane region IV by an alanine increased the affinities of sumatriptan, methysergide and 8-hydroxy-2-(dipropylamino)tetralin (8-OH-DPAT) 3-4-fold and substitution by a methionine increased the affinities of methysergide and methiothepin 2- and 3-fold, respectively. Substitution of amino acid S334 in transmembrane region VI by an alanine increased the affinity of 8-OH-DPAT 5-fold. In accordance with this, the EC50 value of 8-OH-DPAT was decreased 7-fold. This suggests that the serine at position 334 causes steric hindrance for 8-OH-DPAT binding that is lost in the S334A mutant. Mutation of F354 in transmembrane region VII, which differs between receptor subtypes, increased the affinity of methiothepin 2-3-fold but the affinities of the other compounds tested were essentially unchanged.

Cerebral dura mater and cephalalgia: relationships between mast cells and catecholaminergic nerve fibers in the rat

The aim of the present study was to examine whether mast cells have the same variations as the related catecholaminergic nerve fibers. Chemical sympathectomy or surgical removal of right superior cervical ganglion induced a rapid decrease of fluorescence in both nerve fibers and mast cells, as confirmed by quantitative analysis (nerve fibers 19 +/- 1.1 vs 1.3 +/- 0.6; mast cell 10.8 +/- 1.9 vs 2.1 +/- 0.3). The results of quantitative analysis after nerve fiber stimulation (electrical), however, showed an increase of the fluorescence in both the nerve fibers and the mast cells (nerve fibers 43.4 +/- 2.4; mast cells 18.6 +/- 1.6). Moreover, we found that the basal zone is more innervated (regarding catecholaminergic nerve fibers) than the apical one, and that the fluorescence level decreases passing from the vasal zone to the perivasal and intervasal zones. Further studies are needed in order to clarify the role of fluorescent nerve fibers and mast cells of cerebral dura mater in cephalalgia.

In-patient treatment of chronic daily headache using dihydroergotamine: a long-term follow-up study

BACKGROUND

The treatment of chronic daily headache (CDH) due to medication overuse remains a common and difficult problem. For selected patients refractory to outpatient management we have used a treatment protocol using dihydroergotamine (DHE) as introduced by Raskin, during a brief (typically 48 hours) in-patient stay. While many studies have documented the short-term efficacy of the DHE protocol, there are limited data on its long-term effects. The purpose of this study was to evaluate quality of life, at three months post treatment and the present time.

METHODS

A retrospective chart review of all patients admitted for the DHE protocol from 1991 to 1996 revealed 174 cases. Of these, 132 patients were interviewed by phone.

RESULTS

The DHE protocol was shown to decrease headache frequency, severity, headache medication use, and absences from work both at three months and the time of interview.

CONCLUSION

This study has the largest patient base and the longest follow-up period for the use of DHE for CDH. The results confirm that the DHE protocol is helpful in breaking the cycle of CDH, although the long-term outcomes of this study are more conservative than other studies have reported.

Agonistic properties of alniditan, sumatriptan and dihydroergotamine on human 5-HT1B and 5-HT1D receptors expressed in various mammalian cell lines

1. Alniditan, a novel migraine abortive agent, is a potent 5-HT1B/5-HT1D receptor agonist of nM affinity. We compared the agonistic properties of alniditan, sumatriptan and dihydroergotamine on the cloned human 5-HT1B receptor expressed at 200 fmol mg(-1) protein (Bmax) in non-induced L929sA cells, at 740 fmol mg(-1) protein in HEK 293 and at 2300 fmol mg(-1) protein in mIFNbeta-induced L929sA cells, and on the human cloned 5-HT1D receptor expressed in C6 glioma cells (Bmax 780 fmol mg(-1) protein). 2. Sodium butyrate treatment increased the expression level of human (h)5-HT1B receptors in HEK 293 cells and h5-HT1D receptors in C6 glioma cells approximately 3 fold, the binding affinities of [3H]-5-HT and [3H]-alniditan were unaffected. 3. Agonistic properties were evaluated based on inhibition of cyclic AMP accumulation in the cells after stimulation of adenylyl cyclase by forskolin or isoproterenol. Alniditan, sumatriptan and dihydroergotamine were full agonists at the hS-HT1B receptor (IC50 values were 1.7, 20 and 2 nM, respectively in HEK 293 cells) and hS-HT1D receptors (IC50 values of 1.3, 2.6 and 2.2 nM, respectively). At the h5-HT1B receptor the agonist potency of the compounds slightly increased with higher receptor density. The opposite was seen for antagonists (ocaperidone, risperidone and ritanserin). 4. This comparative study demonstrated that alniditan was 10 times more potent than sumatriptan at the h5-HT1B receptor, and twice as potent at the h5-HT1D receptor. Dihydroergotamine was more potent an agonist at the h5-HT1B receptor when expressed at high and low level in L929sA cells (but not in HEK 293 cells), and was less potent at the hS-HT1D receptor.

Comparison of more and less lipophilic serotonin (5HT1B/1D) agonists in a model of trigeminovascular nociception in cat

The trigeminovascular system consists of bipolar neurons innervating pain-producing intracranial structures, such as the superior sagittal sinus (SSS), and projecting to the medullary and upper cervical dorsal horn second order neurons. Zolmitriptan is a newly developed 5HT1B/1D receptor agonist with both peripheral and central sites of action in the trigeminovascular system due to greater lipophilicity relative to the more hydrophilic antimigraine compound sumatriptan. Given that we have seen electrophysiological and autoradiographic binding data to suggest that the compound may inhibit activity at second-order neurons this study was designed to examine whether such an effect could be demonstrated in a population of trigeminal neurons using Fos immunohistochemistry. Cats were anesthetised with alpha-chloralose (60 mg/kg intraperitoneal then 20 mg/kg intravenous maintenance) with all surgery being conducted using halothane (1-3%). The animals were prepared for physiological monitoring, including blood pressure, heart rate, rectal temperature, and end-expiratory CO2. They were intubated, ventilated, and paralyzed with gallamine triethiodide (6 mg/kg i.v.). A midline craniotomy was performed to expose the sinus for electrical stimulation using hook electrodes. Twenty-four hours after completion of the surgical procedures the animal was ready for treatment. Vehicle, sumatriptan (85 micrograms/kg), or zolmitriptan (30 micrograms/kg) was administered and the SSS was stimulated (250 microseconds, 100 V at 0.3 Hz) for 1 h. Following an additional 1 h the animal was perfused and immunohistochemistry was used to detect the protein product of the immediate early gene c-Fos. We compared the dorsal horns of the medulla (trigeminal nucleus caudalis) and the C1 and C2 cervical spinal cords in control animals with those receiving zolmitriptan or sumatriptan. We noted a significant reduction in Fos expression after treatment with zolmitriptan but no effect with sumatriptan. Given that zolmitriptan accesses central neurons and that the method of stimulation we have employed would bypass peripheral trigeminal mechanisms it is likely that the reduction in second-order trigeminal neuronal activity was due to a direct inhibitory effect of the compound on those cells. These neurons form a possible site for the treatment of acute attacks of migraine.

Cortical spreading depression-associated hyperemia in rats: involvement of serotonin

We investigated whether the vasoactive neurotransmitter serotonin (5-HT) is involved in cortical spreading depression (CSD)-associated hyperemia in the rat. We focused on the 5-HT2 receptor, which is engaged in 5-HT induced small arteriolar relaxation in cats, as well as on the 5-HT1D/1B receptor, the binding site of the potent antimigraine drug sumatriptan. In male barbiturate anaesthetized Wistar rats (n=25) CSDs were elicited by brain topical application of 1 M KCl, and the DC-potential and regional cerebral blood flow (rCBF, by Laser Doppler flowmetry) were measured over the same hemisphere through dura and thinned bone, respectively. Intravenous application of 8 mg/kg of the 5-HT2A/2C receptor antagonist ritanserin (group I; n=8) significantly reduced the hyperperfusion amplitude during CSD by approximately 44% (p<0.05, from 342+/-124 to 194+/-97%, baseline before CSD=100%), and prolonged its duration by approx. 30%. Vehicle alone (group II; n=4) did not affect CSD hyperperfusion. The highly selective 5-HT1D/1B receptor agonist 311C90 was given in two doses: 100 micrograms/kg i.v. (n=5) had no effect on CSD hyperperfusion, while 800 micrograms/kg (n=5) increased hyperperfusion significantly (p<0.05, from 224+/-86 to 310+/-148%). We conclude that serotonin is, probably via 5-HT2 receptors, involved in the modulation of the regional cerebral blood flow increase during CSD. Novel highly selective receptor antagonists may help to discriminate the differential contribution of various 5-HT receptor subspecies.

Chemical stimulation of the intracranial dura induces enhanced responses to facial stimulation in brain stem trigeminal neurons

Chemical activation and sensitization of trigeminal primary afferent neurons innervating the intracranial meninges have been postulated as possible causes of certain headaches. This sensitization, however, cannot explain the extracranial hypersensitivity that often accompanies headache. The goal of this study was to test the hypothesis that chemical activation and sensitization of meningeal sensory neurons can lead to activation and sensitization of central trigeminal neurons that receive convergent input from the dura and skin. This hypothesis was investigated by recording changes in the responsiveness of 23 [16 wide-dynamic range (WDR), 5 high threshold (HT), and 2 low threshold (LT)] dura-sensitive neurons in nucleus caudalis to mechanical stimulation of their dural receptive fields and to mechanical and thermal stimulation of their cutaneous receptive fields after local application of inflammatory mediators or acidic agents to the dura. Responses to brief chemical stimulation were recorded in 70% of the neurons; most were short, lasting the duration of the stimulus only. Twenty minutes after chemical stimulation of the dura, the following changes occurred: 1) 95% of the neurons showed significant increases in sensitivity to mechanical indentation of the dura: their thresholds to dural indentation changed from 1.57 to 0.49 g (means, P < 0.0001), and the response magnitude to identical stimuli increased by two- to fourfold; 2) 80% of the neurons showed significant increases in cutaneous mechanosensitivity: their responses to brush and pressure increased 2.5- (P < 0.05) and 1. 6-fold (P < 0.05), respectively; 3) 75% of the neurons showed a significant increase in cutaneous thermosensitivity: their thresholds to slow heating of the skin changed from 43.7 +/- 0.7 to 40.3 +/- 0.7 degrees C (P < 0.005) and to slow cooling from 23.7 +/- 3.3 to 29.2 +/- 1.8 degrees C (P < 0.05); 4) dural receptive fields expanded within 30 min and cutaneous receptive fields within 2-4 h; and 5) ongoing activity developed in WDR and HT but not in LT neurons. Application of lidocaine to the dura abolished the response to dural stimulation but had minimal effect on the increased responses to cutaneous stimulation (suggesting involvement of a central mechanism in maintaining the sensitized state). Antidromic activation (current of <30 muA) of dura-sensitive neurons revealed projections to the hypothalamus, thalamus, and midbrain. These findings suggest that chemical activation and sensitization of dura-sensitive peripheral nociceptors could lead to enhanced responses in central neurons and that this central sensitization therefore could result in extracranial tenderness (mechanical and thermal allodynia) in the absence of extracranial pathology. The projection targets of these neurons suggest a possible role in mediating the autonomic, endocrine, and affective symptoms that accompany headaches.

Repression of the calcitonin gene-related peptide promoter by 5-HT1 receptor activation

We have investigated the control of calcitonin gene-related peptide (CGRP) expression by a serotonergic agonist that is related pharmacologically to currently used antimigraine drugs. During migraines, CGRP levels are elevated but then returned to normal by a 5-HT1 receptor agonist, sumatriptan. However, neither the molecular nor cellular targets of this drug are known. Trigeminal neurons are the major source of cerebrovascular CGRP, and thus we have used trigeminal primary cultures and the neuronal-like CA77 thyroid C-cell line as a model. We first demonstrate that sumatriptan and another 5-HT1 agonist, CGS 12066A (CGS), cause a robust and prolonged increase with oscillations in intracellular calcium in CA77 cells. CGS caused a similar increase in trigeminal cultures. We then show that CGS treatment leads to a decrease in CGRP mRNA levels in the CA77 cells. This decrease is attributable to the repression of promoter activity through two discrete elements: (1) the cAMP-responsive region, via a cAMP-independent mechanism; and (2) the cell-specific enhancer, which binds the upstream stimulatory factor helix-loop-helix protein and a cell-specific activator. These results demonstrate that activation of the endogenous 5-HT1 receptor is coupled to calcium signaling pathways and leads to inhibition of CGRP gene transcription.

The selectivity of MDL 74,721 in models of neurogenic versus vascular components of migraine

MDL 74,721 (R)-2-(N1,N1-dipropylamino)-8-methylaminosulfonylmethyl-1,2,3,4-te trahydronaphthalene, a sulfonamidotetralin, has been found to exhibit a 10,000-fold greater potency in neurogenic versus vascular models of migraine. Sumatriptan, a relatively pure 5-HT1D/5-HT1B receptor agonist, also showed higher potency versus neurogenic inflammation. However, for sumatriptan the potency difference (100-fold) in the two pathophysiological models was less pronounced than seen for MDL 74,721. The affinity profile of MDL 74,721 at 5-HT1 receptor subtypes may in part explain its ability to differentiate these two physiological responses. MDL 74,721 demonstrated nanomolar affinity for 5-HT1A (12.7 +/- 0.3 nM) and 5-HT1D (41.3 +/- 10.9 nM) but considerably lower affinity for 5-HT1B receptors (> 1000 nM). Serotonin-like activity was seen in in vitro functional assays including inhibition of forskolin-stimulated cAMP accumulation in human 5-HT1D receptor-transfected fibroblasts or eliciting vasoconstriction in isolated human pial arteries. The intrinsic activity (relative to 5 - HT[E(Amax)]) and affinity (pD2) for the human cerebrovascular 5-HT receptors were: 5-HT (100%, 7.51 +/- 0.09), sumatriptan (94%, 6.85 +/- 0.1) and MDL 74,721 (66%, 5.70 +/- 0.23). In anaesthetised cats, treatment with MDL 74,721 resulted in a dose-related reduction in the percentage of carotid flow going through the arteriovenous anastomoses to the lungs, with an ED50 of 0.3 mg/kg i.v., the same as sumatriptan. However, in the guinea-pig neurogenic model, MDL 74,721 inhibited plasma protein extravasation with an ED50 of 0.023 microg/kg compared to 2.5 microg/kg for sumatriptan. MDL 74,721 was also effective in this model (in rats) after oral administration. In conclusion, MDL 74,721 demonstrates a preclinical profile consistent with anti-migraine efficacy. Its marked preference for inhibiting neurogenic inflammation makes this compound a useful tool for assessing the relative contribution of this pathophysiological mechanism to the human disease state.

Pre-clinical pharmacology of zolmitriptan (Zomig; formerly 311C90), a centrally and peripherally acting 5HT1B/1D agonist for migraine

Zolmitriptan (Zomig; formerly 311C90) is a novel 5-hydroxytryptamine (5HT)1B/1D receptor agonist with proven efficacy in the acute treatment of migraine with or without preceding aura. The drug differs from presently available members of this drug class in that it combines 5HT1B/1D receptor partial agonist activity with robust oral pharmacokinetics and an ability to inhibit trigeminovascular activation centrally as well as peripherally in preclinical studies. Consistent with its selectivity for 5HT1B/1D receptors, zolmitriptan produces constriction of various isolated blood vessels, most notably cranial arteries. In anaesthetized animals, these vascular effects manifest as a selective constriction of cranial arterio-venous anastomoses resulting in a redistribution of carotid arterial blood flow. This effect is produced without significant effects on heart rate, blood pressure or blood flow to the brain, heart or lungs. Zolmitriptan also inhibits trigeminal-evoked increases in cerebral blood flow in anaesthetized cats and blocks trigeminal-evoked plasma protein extravasation in the dura of guinea-pigs. These actions are consistent with a pre-junctional inhibition of neuropeptide release from perivascular afferents of the trigeminal nerve, as confirmed by independent studies showing that zolmitriptan blocks elevations of calcitonin-gene-related peptide in jugular venous blood during electrical stimulation of the trigeminal ganglion. In all of these effects, zolmitriptan is three to four times more potent than sumatriptan, but produces the same maximum response. Zolmitriptan crosses the intact blood-brain barrier to inhibit trigeminovascular activation in the brainstem. This was shown initially by the ability of the drug to block a brainstem reflex provoking vasoactive intestinal peptide release from the VIIth cranial (facial) nerve during trigeminal stimulation. Subsequent ex vivo autoradiography confirmed that intravenously injected [3H]zolmitriptan labels a discrete population of cells in the trigeminal nucleus caudalis (TNC) and nucleus tractus solitarius. Direct evidence for a central neuromodulatory effect of zolmitriptan was provided by electrophysiological experiments which clearly demonstrated that the drug inhibits the excitability of cells in the TNC after systemic administration. This novel pre-clinical profile not only distinguishes zolmitriptan from sumatriptan, but raises intriguing questions about the clinical relevance of a dual action. Studies to date show that zolmitriptan indeed modulates cranial sensory processing in humans, yet central side-effects are no different from sumatriptan. This property may account for the remarkable consistency in clinical efficacy observed in clinical trials.

Convergence of occipital nerve and superior sagittal sinus input in the cervical spinal cord of the cat

Co-existence of facial and occipital pain may occur in occipital neuralgia, migraine and cluster headache; suggesting convergence of trigeminal and cervical afferents. Such convergence has been shown in humans and other animals, but the site and extent of this are uncertain. In anaesthetized adult cats, the superior sagittal sinus and occipital nerve were stimulated electrically, and extracellular recordings made in the dorsolateral area of the upper cervical cord using glass-coated tungsten electrodes. Of 49 units in 10 cats, 33 (67%) had input from the superior sagittal sinus and the occipital nerve. Thirteen (27%) had superior sagittal sinus input and 3 (6%) had occipital nerve input. Convergent receptive fields were identified mechanically in 7 units. These experiments in cats show convergent input from occipital nerve and superior sagittal sinus on dorsolateral area units in two-thirds of cases studied. This experimental site of trigeminocervical convergence may relate to referral of pain in occipital neuralgia and other headaches.

Neuroanatomical localization, pharmacological characterization and functions of CGRP, related peptides and their receptors

Calcitonin generelated peptide (CGRP) is a neuropeptide discovered by a molecular approach over 10 years ago. More recently, islet amyloid polypeptide or amylin, and adrenomedullin were isolated from human insulinoma and pheochromocytoma respectively, and revealed between 25 and 50% sequence homology with CGRP. This review discusses findings on the anatomical distributions of CGRP mRNA, CGRP-like immunoreactivity and receptors in the central nervous system, as well as the potential physiological roles for CGRP. The anatomical distribution and biological activities of amylin and adrenomedullin are also presented. Based upon the differential biological activity of various CGRP analogs, the CGRP receptors have been classified in two major classes, namely the CGRP1 and CGRP2 subtypes. A third subtype has also been proposed (e.g. in the nucleus accumbens) as it does not share the pharmacological properties of the other two classes. The anatomical distribution and the pharmacological characteristics of amylin binding sites in the rat brain are different from those reported for CGRP but share several similarities with the salmon calcitonin receptors. The receptors identified thus far for CGRP and related peptides belong to the G protein-coupled receptor superfamily. Indeed, modulation of adenylate cyclase activity following receptor activation has been reported for CGRP, amylin and adrenomedullin. Furthermore, the binding affinity of CGRP and related peptides is modulated by nucleotides such as GTP. The cloning of various calcitonin and most recently of CGRP1 and adrenomedullin receptors was reported and revealed structural similarities but also significant differences to other members of the G protein-coupled receptors. They may thus form a new subfamily. The cloning of the amylin receptor(s) as well as of the other putative CGRP receptor subtype(s) are still awaited. Finally, a broad variety of biological activities has been described for CGRP-like peptides. These include vasodilation, nociception, glucose uptake and the stimulation of glycolysis in skeletal muscles. These effects may thus suggest their potential role and therapeutic applications in migraine, subarachnoid haemorrhage, diabetes and pain-related mechanisms, among other disorders.

Syndromes of posttraumatic neurological deterioration in children with no focal lesions revealed by cerebral imaging: evidence for a trigeminovascular pathophysiology

PURPOSE

To explain the pathophysiology of the neurological deterioration that occurs after trivial head injuries in children and that is not caused by focal structural brain damage. Symptoms and/or signs include headache, confusion, drowsiness, vomiting, hemiparesis, cortical blindness, and seizures.

CONCEPT

We propose that children who are susceptible to such neurological attacks have an unstable "trigeminovascular reflex," which is activated by craniofacial trauma.

RATIONALE

After posttraumatic mechanical stimulation and activation of a defective or immature "excitable" trigeminovascular system, release of perivascular vasodilatory peptides causes cerebral hyperemia, which underlies the neurological deterioration.

DISCUSSION

The original assumption that underlying cerebral edema was responsible for these phenomena has been proven incorrect by computed tomography. Subsequent proposed pathophysiological mechanisms include cortical spreading depression and trauma-triggered migraine. Recent research has implicated the trigeminovascular pathways in both these conditions and documented that head trauma can be associated with noncongestive cerebral hyperemia (i.e., not causing swelling). Thus, we propose that head trauma activates trigeminal nerve endings in face, scalp, dura, or cortex and, via a reflex, causes intracranial vasodilation and cerebral hyperemia. Drugs that block trigeminovascular activation might offer a benefit.

Effects of the 5-HT1 receptor agonists, sumatriptan and CP 93,129, on dural arterial flow in the rat

The blood flow in and around the medial meningeal artery (dural arterial flow) was recorded in the exposed parietal dura mater encephali of the anesthetized rat using laser Doppler flowmetry. Local electrical stimulation of the dura mater (pulses of 0.5 ms delivered at 7.5-17.5 V and 5 or 10 Hz for 30 s) caused temporary increases in dural arterial flow. The effects of the 5-HT1 receptor agonists sumatriptan and CP 93,129 on the basal flow and the electrically evoked increases in flow were examined. Topical administration of undiluted sumatriptan (12 mg/ml) lowered the basal and the evoked flow by 20% on average. Systemic (i.v.) administration of sumatriptan (0.24, 0.72 and 3.6 mumol/kg) caused a short-lasting reduction of the evoked flow increases only at the higher doses while the basal flow was not significantly altered. Systemic administration of CP 93, 129 (0.46 and 4.6 mumol/kg) caused no significant changes of the basal and the evoked flow. At a dose of 23 mumol/kg CP 93,129 lowered the basal flow by 20% and the evoked flow by 30% for 20 min. The systemic arterial pressure was not significantly altered by sumatriptan and CP 93,129 within the whole range of doses. It is suggested that sumatriptan and CP 93,129 at high doses exert inhibitory effects on those fine afferent nerve fibers which release the calcitonin gene-related peptide, since this neuropeptide mediates the evoked increases in dural arterial flow.

Expression of calcitonin gene-related peptide1 receptor mRNA in human trigeminal ganglia and cerebral arteries

Reverse transcriptase polymerase chain reaction (RT-PCR) using primers for the recently cloned human CGRP1 receptor detected mRNA expression of CGRP1 receptors in trigeminal ganglia and cerebral vessels, obtained at autopsy or during neurosurgical tumor resections. An RT-PCR product of the expected size (339 bp) was seen in cerebral arteries, both in the presence and in the absence of endothelium and in trigeminal ganglia. Sequence analysis of the RT-PCR product of the published sequence showed 100% homology with the human CGRP1 receptor. The presence of the CGRP1 receptor mRNA in human trigeminal ganglia and cerebral blood vessels, indicates the occurrence of both prejunctional (trigeminal) and postjunctional location (blood vessels) of the CGRP1 receptor.

Intravenous chlorpromazine versus intramuscular sumatriptan for acute migraine

OBJECTIVE

To establish whether there is any difference in the efficacy of a chlorpromazine regimen and a sumatriptan regimen for the management of the pain of acute severe migraine.

SETTING

Two urban teaching hospital emergency departments.

METHODS

Prospective, randomised, unblinded, crossover trial. All patients received intravenous metoclopramide 10 mg and 1000 ml of normal saline over 1 h; 20 were then randomised to receive intramuscular sumatriptan 6 mg and 23 to receive intravenous chlorpromazine, 12.5 mg increments to a maximum of 37.5 mg. Response to treatment was measured using visual analogue pain scales.

RESULTS

No difference in efficacy between the sumatriptan regimen and the chlorpromazine regimen was found. Adverse effects were mild and equally distributed between the groups.

CONCLUSIONS

The chlorpromazine and sumatriptan regimens studied are both very effective for the relief of the headache of severe migraine.

The novel anti-migraine agent rizatriptan inhibits neurogenic dural vasodilation and extravasation

These studies in anaesthetised rats showed, using intravital microscopy, that the novel anti-migraine agent, rizatriptan, significantly reduced electrically stimulated dural vasodilation but had no effect on increases in dural vessel diameter produced by exogenous substance P or calcitonin gene-related peptide (CGRP). Rizatriptan also significantly inhibited dural plasma protein extravasation produced by high intensity electrical stimulation of the trigeminal ganglion. We suggest that rizatriptan inhibits the release of sensory neuropeptides from perivascular trigeminal nerves to prevent neurogenic vasodilation and extravasation in the dura mater. These prejunctional inhibitory effects may be involved in the anti-migraine action of rizatriptan.

Sumatriptan inhibits neurogenic vasodilation of dural blood vessels in the anaesthetized rat--intravital microscope studies

This study used intravital microscopy to measure the diameter of dural arteries in anaesthetized rats. Electrical stimulation of the surface of a closed cranial window produced increases in dural vessel diameter which were blocked by the CGRP receptor antagonist human-alpha CGRP(8-37) but unaffected by the NK1 receptor antagonist RP67580. Sumatriptan (3 and 10 mg kg-1, i.v.) significantly reduced the response to electrical stimulation. In contrast, sumatriptan (3 mg kg-1) had no effects on the response to exogenously administered CGRP. These results indicate that neurokinins play no role in neurogenic vasodilation in this preparation and that neurogenic vasodilation in rat dural vessels is mediated predominantly by CGRP. Furthermore, the data indicate that sumatriptan attenuates neurogenic vasodilation, probably by inhibiting the release of CGRP from perivascular trigeminal nerve endings innervating the dura. These experimental data parallel the clinical findings that CGRP levels are elevated in migraine and normalized, concomitantly with headache relief, by sumatriptan.

Release of histamine from dural mast cells by substance P and calcitonin gene-related peptide

The aim of the present study was to examine if the neuropeptides substance P (SP), calcitonin gene-related peptide (CGRP), neuropeptide Y (NPY) and vasoactive intestinal peptide (VIP) can stimulate histamine release from mast cells in the dura mater and thereby play a role in cranial vasoregulation and local neurogenic inflammation. Dura mater mast cells were compared with peritoneal mast cells in the rat. Histamine was released from dura mater mast cells by compound 48/80, SP and CGRP but from peritoneal mast cells only by compound 48/80 and SP. NPY and VIP released quite small amounts of histamine from dural mast cells. The release of SP and CGRP from rat dura mater mast cells was blocked by the receptor antagonists FK888 and CGRP8-37 respectively, suggesting receptor mediated release mechanisms. None of the stimuli released histamine from human or porcine dural mast cells, possibly because the sampling procedure injures and incapacitates the cells.

Direct evidence for central sites of action of zolmitriptan (311C90): an autoradiographic study in cat

The trigeminovascular system consists of bipolar neurons which innervate pain-sensitive intracranial structures and projecting to neurons in the superficial laminae of the caudal trigeminal nucleus and of the dorsal horns of C1 and C2. The serotonin (5HT1B/D) agonist zolmitriptan (311C90) has been shown to be effective in the treatment of acute attacks of migraine and experimental data suggest that it may have both peripheral and central sites of action. This study sought to further investigate possible central effects of zolmitriptan (311C90) by examining its distribution in the central nervous system. Specific binding of [3H]-zolmitriptan was determined both ex vivo and in vitro in the cat brain. For the ex vivo studies, cats were anaesthetized with halothane and alpha-chloralose (60 mg/kg intraperitoneal). A femoral vein catheter was inserted for injection of the [3H]-zolmitriptan and then 1 h after injection the brain removed. For the in vitro studies fresh frozen brain slices were incubated with labelled and masking concentrations of zolmitriptan. The distribution of [3H]-zolmitriptan was determined using quantitative autoradiographic methods. The in vitro work demonstrated specific binding of [3H]-zolmitriptan in the superficial laminae of the trigeminal nucleus caudalis and dorsal horns of the C1 and C2 cervical spinal cord. The density of binding was 53 +/- 9 fmol/mg for the trigeminal nucleus caudalis, 47 +/- 7 fmol/mg for C1 and 50 +/- 6 fmol/mg for C2. The ex vivo work demonstrated binding in anatomically identical areas which was less dense than that seen with the in vitro method. These data confirm the existence of a population of receptors that specifically bind zolmitriptan following systemic administration. These receptors may, in part, be responsible for its clinical efficacy and reinforce the importance of central trigeminal neurons as a possible site of action of anti-migraine drugs.

Neurological episodes after minor head injury and trigeminovascular activation

Children appear particularly susceptible to severe but reversible neurological symptoms and/or signs after minor head injury; these include headache, confusion, drowsiness, vomiting, hemiparesis, cortical blindness, or seizures. Significantly, these neurological episodes are not associated with any identifiable structural brain abnormality on neuro-imaging. We propose that the cause of this condition is a reactive hyperaemia, a 'benign hyperaemic encephalopathy' mediated via activation of the trigeminovascular system.

Differential distribution of [3H]sumatriptan binding sites (5-HT1B, 5-HT1D and 5-HT1F receptors) in human brain: focus on brainstem and spinal cord

We report on the autoradiographic distribution of 5-HT1B, 5-HT1D and 5-HT1F receptor subtypes in human brain, focusing on the brainstem and cervical spinal cord. We have used [3H]sumatriptan as a radioligand in the presence of suitable concentrations of 5-CT (5-carboxamidotryptamine) to define 5-HT1F receptors, and ketanserin, to discriminate between 5-HT1B and 5-HT1D receptors. In the brainstem the highest concentrations of [3H]sumatriptan binding sites were seen in substantia nigra. The spinal trigeminal nucleus, substantia gelatinosa of the spinal cord, nucleus of the tractus solitarius and periaqueductal grey, also showed significant levels of [3H]sumatriptan binding sites. In the brainstem and spinal cord the total population of 5-CT-insensitive receptors, corresponding to 5-HT1F receptors, ranged from 9.8% in the periaqueductal grey to 53.4% in the substantia gelatinosa. This population represented 67.0% of binding in layer V of the frontal cortex. The decrease in [3H]sumatriptan binding in the presence of 200 nM ketanserin, indicative of the presence of 5-HT1D receptors, was very limited throughout the human brain, only reaching 20% of total specific binding over the periaqueductal grey. The proportion of [3H]sumatriptan binding sites displaced by 5-CT and insensitive to ketanserin, corresponding to 5-HT1B receptors, was, in general, the most abundant, ranging from 43.8% in substantia gelatinosa to 69.9% in the periaqueductal grey. Significant levels of 5-HT1B and 5-HT1D receptors found in migraine control pain areas suggest their involvement in antinociceptive mechanisms.

Differential effects of 5-HT1B/1D receptor agonists on neurogenic dural plasma extravasation and vasodilation in anaesthetized rats

These studies compared the effects of the 5-HT1B/1D receptor agonists sumatriptan, CP-122 288 ((R)-N-methyl-[3-(1-methyl-2-pyrrolidinylmethyl)-1H-indol-5-yl] methanesulphonamide succinate) and CP-93 129 (3-(1,2,5,6-tetrahydropyrid-4-yl)pyrrolo[3,2-b]pyrid-5-one dihydrochloride) on neurogenic dural extra-vasation and vasodilation in anaesthetized rats. Dural extravasation, evoked by high intensity (1.2 mA) stimulation of the trigeminal ganglion, was measured using the radioactive plasma marker 125I-labelled bovine serum albumin. Dural vasodilation produced by lower intensity (50-300 microA) stimulation of trigeminal fibres, was measured through a closed cranial window using intravital microscopy. All compounds inhibited dural extravasation (rank order of potency: CP-122 288 > > sumatriptan > CP-93 129) and dural vasodilation (rank order of potency: CP-93 129 > > sumatriptan = CP-122 288). Comparison of the potency of these compounds with their potencies in an in vitro functional model, agonist-induced [35S]GTP gamma S binding, suggests that blockade of dural extravasation was consistent with an action at rat 5-HT1D receptors, but activity at another, unknown, "extravasation receptor" could also be involved. In contrast, inhibition of dural vasodilation was consistent with an action at rat 5-HT1B receptors. We suggest that in our preparations, production of dural vasodilation involves activation of trigeminal A delta-fibres whereas production of dural extravasation involves activation of trigeminal C-fibres. The differential effects of compounds on dural extravasation and vasodilation may therefore be due to the different receptor subtypes involved and to the selective localization of these subtypes on different populations of trigeminal sensory fibre.

How do the currently used prophylactic agents work in migraine?

Since migraine attacks are often frequent they require management with agents that reduce their number. Such agents, although often effective, are mechanistically ill-understood. They have been suggested to work through four main mechanisms, 5HT2 antagonism, modulation of plasma protein extravasation, modulation of central aminergic control mechanisms and membrane stabilizing effects through actions at voltage-sensitive channels. The evidence for these mechanisms, except plasma protein extravasation (see Cutrer, this supplement) is examined in the light of current thoughts concerning the pathophysiology of migraine.

Possible mechanisms of valproate in migraine prophylaxis

Valproate has been shown to be an effective prophylactic treatment in migraine. Investigation of the mechanism of its antimigraine action is difficult due to the broad range of its biochemical effects and the complex nature of migraine pathophysiology. Valproate increases brain GABA levels and, in doing so, may suppress migraine-related events in the cortex, perivascular parasympathetics or trigeminal nucleus caudalis. There is experimental evidence that it suppresses neurogenic inflammation and directly attenuates nociceptive neurotransmission. In addition, valproate reportedly alters levels of excitatory and inhibitory neurotransmitters and exerts direct effects on neuronal membranes in vitro. Valproate's observed effect may ultimately result from a combination of actions at different loci.

Trigeminovascular stimulation in conscious rats

Intracisternal infusion of capsaicin was used to induce intracranial trigeminovascular stimulation in conscious rats. Both behaviour and trigeminal nucleus caudalis c-fos expression were examined. Exploratory behaviour was dose-dependently reduced and different types of behaviours were induced with various doses of capsaicin. Head grooming and scratching show that intracranial activation of trigeminal afferents can be referred as extracranial trigeminal stimulation. Analysis of behaviour exhibited during trigeminovascular stimulation may provide a powerful tool to study effects of central acting anti-migraine drugs.

On the origin of headaches

Headache is one of the most common types of pain, but its causes remain poorly understood. The long-standing idea that some headaches, particularly migraine, might be caused by cerebral or cranial vasodilation has failed to find support in recent studies. Alternative hypotheses have focused on other processes that might be capable of activating or sensitizing sensory nerve fibres that innervate the blood vessels of the intracranial meninges.